Untangling the relationship between glucose and blood vessel function in the eye

My younger brother was four years old when he was diagnosed with type 1 diabetes mellitus. A previously well child, there were no obvious signs that his pancreas was under an insidious attack from his own immune system until his insulin ran out and he experienced dangerously high blood glucose levels.

Like the diabetes itself, the complications of diabetes are hard to detect until considerable damage has already been done. My own research is related to a particular complication in the eyes called diabetic retinopathy. Diabetic retinopathy is the most common cause of blindness in working-age adults in developed countries and is an increasing problem in the developing world. We need eye tests that can detect eye damage at an early stage so we can take action to reduce the risk of vision loss later down the track.

Blood vessels in the eye dilate when stimulated with flicker light to increase the supply of oxygen. Our research group has previously shown that blood vessel dilation during flicker light stimulation is reduced in people with diabetes. This is the case even in those without any obvious signs of diabetic retinopathy. It is unclear whether these reduced responses are directly caused by high blood glucose or are a result of progressive damage over time.

To better understand the relationship between high blood glucose and the function of blood vessels in the eye, the Centre for Eye Research Australia with St Vincent’s Hospital (Melbourne) have initiated a study to compare the function of these blood vessels at normal and high blood glucose levels in people with type 1 diabetes. Previous studies have shown that high blood glucose impairs the function of blood vessels in other body locations, so we expect similar findings in the eye.

The second major objective of our study is to test whether vitamin C can stop blood vessels in the eye and other body locations becoming dysfunctional during periods of high blood glucose. Vitamin C is an important part of our diet and has been previously shown to benefit certain types of macular degeneration, another major cause of blindness. If high blood glucose impairs blood vessel function by increasing oxidative stress as we suspect, antioxidants like vitamin C could help reduce oxidative stress and normalise the function of these blood vessels.

If we can prove that vitamin C protects blood vessels in the eye from the effects of high blood glucose, this should lead to a larger clinical trial in people with diabetes to test whether antioxidants can reduce the risk of diabetic complications like diabetic retinopathy.

Participation in this research is relatively straightforward. It involves 2 visits of 3-4 hours to St Vincent’s Hospital (Melbourne) where we would non-invasively test the function of blood vessels in the eyes and the forearm while the blood glucose is fixed at normal (5.6 mmol/l) and high (15 mmol/l) levels. At one visit we would give vitamin C and at the other we would give a placebo that looks the same but is inactive. We would insert intravenous lines in veins in both arms for insulin, glucose and vitamin C and to easily check blood glucose levels. We would also do an electrocardiogram (ECG) of the heart, photos of the retina at the back of the eye and a full laboratory workup.

We are offering participants $50 and a meal at the end of each visit.

If you or someone you know has type 1 diabetes without any diabetic complications or other medical issues, please get in contact with me at 03 9929 8363 or jnoonan@student.unimelb.edu.au so that we can carry out this important research.

This research is supported by a Type 1 Diabetes Pilot and Feasibility Grant from the Juvenile Diabetes Research Foundation.

About the Author

Jonathan Noonan is a clinician with an interest in ophthalmology. He is currently in the final year of his PhD, which is investigating the mechanisms of impaired blood vessel function in the eyes of people with type 1 diabetes. Read more by this author →